The skin contains numerous sensory receptors which receive information from the outside environment. The sensory receptors of the skin are concerned with at least five different senses: pain, heat, cold, touch, and pressure. The five are usually grouped together as the single sense of touch in the classification of the five senses
of the whole human body. The sensory receptors vary greatly in terms of structure. For example, while pain receptors are simply unmyelinated terminal branches of neurons, touch
receptors form neuronal fiber nets around the base of hairs and deep pressure receptors consist of nerve endings encapsulated by specialized connective tissues. Receptors also vary in terms of abundance relative to each other. For example, there are far more pain receptors than cold receptors in the body. Finally, receptors vary in terms of the concentration of their distribution over the surface of the body, the fingertips having far more touch receptors than the skin of the back.
Other types of receptors located throughout the whole body, including proprioceptive receptors and visceral receptors, receive information about the body's internal environment
. Proprioceptive or stretch receptors, located in muscles and tendons, sense changes in the length and tension of muscles and tendons and help to inform the central nervous system of the position and movement of the various parts of the body. Each stretch receptor consists of specialized muscle fibers and the terminal branches of sensor neurons. The muscle fibers and sensor neuron endings are very closely associated and are encased in a sheath of connective tissue.
Visceral receptors monitor the conditions of the internal organs. Most responses to their stimulation by an organ are carried out by the autonomic system. Several visceral sensors, however, produce conscious sensations such as nausea, thirst, and hunger.
Touch Receptors are the nerves cells that tell your brain about tactile sensations. There are several types of touch receptors, but they can be divided into two groups. Mechanoreceptors that give the sensations of pushing, pulling or movement, and thermoreceptors that tell you about sensations of temperature.
The mechanoreceptors contain the most types of touch receptors. Free nerve endings inform the brain about pain, and they are located over the entire body. Located in the deep layers of dermis in both hairy and glabrous skin, the pacinian corpuscles detect pressure, telling the brain when a limb has moved. After the brain has told a limb, such as an arm, to move, the pacinian corpuscles tells the brain that that limb has actually moved into the correct position.
The tactile corpuscles of meissner are grouped on the skin of the fingertips, lips, and orifices of the body and nipples. Only stimulated when touched, meissner corpuscles tell the brain the shape and feel of an abject in the hand, or the touch of a kiss. They adjust constantly to the environment, which is why the brain eventually ignores clothing that you are wearing.
Thermoreceptors are the other major group of touch receptors. There are two types of thermoreceptors, the end-bulb of Krause, which detects cold, and Ruffini’s end organ, which detects heat. The end-bulb of Krause can be found in the skin, conjunctiva, lips, and tongue. Ruffini’s end organs are found over the entire body in the skin.